Introduction

Refer to page 12 in these course notes Page 8 in EMMUA 214 where Zone Demarcation is covered in section 4 Hazardous Areas

Area classification is a method of analysing and classifying the environment where explosive gas atmospheres may occur (the classification of areas into zones,) where there may be a risk of ignition and possibly explosion, due to the presence of flammable gas or vapour mixed with air under normal atmospheric conditions. The relevant standard is IEC 60079-10-1 Explosive Gas Atmospheres. So as to facilitate the proper selection and installation of equipment to be used safely in that environment. The classification also takes into account the ignition characteristics of the gas or vapour such as ignition energy (gas group) and ignition temperature (temperature class).

In most practical situations where flammable materials are used, it is difficult to ensure that an explosive gas atmosphere will never occur. It may also be difficult to ensure that equipment will never give rise to a source of ignition. Therefore, in situations where an explosive gas atmosphere has a high likelihood of occurring, reliance is placed on using equipment which has a low likelihood of creating a source of ignition. Conversely, where the likelihood of an explosive gas atmosphere occurring is reduced, equipment constructed with less rigorous requirements may be used.

The area classification should be carried out by those who understand the relevance and significance of properties of flammable materials and those who are familiar with the process and the equipment along with safety, electrical, mechanical and other qualified engineering personnel.

The aim of Area Classification is to reduce to an acceptable level the possibility of a flammable atmosphere and an electrical source of ignition coinciding.

The area classification should be carried out when the initial process and instrumentation line diagrams and initial layout plans are available and confirmed before plant start-up. Reviews should be carried out during the life of the plant.

Area classification, in respect of gases, is concerned with the classification of areas into zones, where there may be a risk of ignition and possibly explosion, due to the presence of flammable gas or vapour mixed with air under normal atmospheric conditions. The relevant standard is IEC 60079-10-1 Explosive Gas Atmospheres.

Area classification is carried out by suitable personnel who are familiar with the processes and equipment along with safety, electrical and mechanical aspects of the installation. Area classification assists in the proper selection and installation of equipment.

Correct evaluation of the area within each zone is aided by additional knowledge relating to: